Dissolution Kinetics of Iron from Low-Grade Mn Ore and Optimization Using Response Surface Methodology

In this study an attempt has been made to increase Mn/Fe ratio in dump Manganese ore fines so that it can be used for the production of ferromanganese. For this purpose non-coking coal was used as reductant and dilute hydrochloric acid as leaching medium for the roasted ore. The effects of acid strength, leaching time, leaching temperature, stirring speed, ore particle size and pulp density have been studied. The dissolution of iron follows the kinetic model 1 ? 2x/3 ? (1 ? x)^2/3 = k_dt. Thus product layer diffusion is the controlling mechanism and the activation energy has been determined to be 26.23 kJ/mol at 40–95 °C. Another set of experiments have been conducted according to 2³ full factorial design, and regression equation for iron dissolution has been developed.     

Determination of the Optimum Conditions for Leaching of Zinc Cathode Melting Furnace Slag in Ammonium Chloride Media

This research is part of a continuing effort to leach zinc from zinc cathode melting furnace slags (ZCMFSs) to produce zinc oxide. The slag with an assay of 68.05 pct Zn was used in ammonium chloride leaching for zinc extraction. In this paper, the effects of influential factors on extraction efficiency of Zn from a ZCMFS were investigated. The Taguchi’s method based on orthogonal array (OA) design has been used to arrange the experimental runs in order to maximize zinc extraction from a slag. The softwares named Excel and Design-Expert 7 have been used to design experiments and subsequent analysis. OA L ₂₅ (5⁵) consisting of five parameters, each with five levels, was employed to evaluate the effects of reaction time (t = 10, 30, 50, 70, 90 minutes), reaction temperature [T = 313, 323, 333, 343, 353 (40, 50, 60, 70, 80) K (°C)], pulp density (S/L = 20, 40, 60, 80, 100 g/L), stirring speed (R = 300, 400, 500, 600, 700 rpm), and ammonium chloride concentration (C = 10, 15, 20, 25, 30 pctwt), on zinc extraction percent. Statistical analysis, ANOVA, was also employed to determine the relationship between experimental conditions and yield levels. The results showed that the significant parameters affecting leaching of slag were ammonium chloride concentration and pulp density, and increasing pulp density reduced leaching efficiency of zinc. However, increasing ammonium chloride concentration promoted the extraction of zinc. The optimum conditions for this study were found to be t ₄: 70 minutes, T ₅: 353 K (80 °C), (S/L)₂: 40 g/L, R ₃: 500 rpm, and C ₄: 25 pctwt. Under these conditions, the dissolution percentage of Zn in ammonium chloride media was 94.61 pct.     

Heap Biooxidation - Bioleachingofa Refractory Gold-Bearing Ore

Abstract

A refractory pyrite/arsenopyrite ore containing 3.7 g/ton of gold finely disseminated in the sulphide matrix was subjected to microbial leaching in a heap containing 120 tons of ore crushed to minus 15 mm. The ore was initially leached by means of acidophilic chemolithotrophic bacteria to oxidize the sulphide minerals and to liberate the gold. About 50% of the sulphide sulphur was oxidized within 90 days. Previous laboratory experiments had shown that such degree of sulphide oxidation resulted in a high gold extraction during the subsequent leaching of the pretreated ore. After the bacterial pretreatment the ore was washed with water and was treated by alkaline solutions until the pH of the heap effluents was established in the range of 9- 10. Then the leaching of the gold was started with solutions containing amino acids of microbial origin and thiosulphate as gold-complexing agents as well as some ions participating in the oxidation and/or complexation of the gold. 70.7% of the gold was leached within 12 days in this way. Silver was leached together with gold. The pregnant solutions were treated by cementation with metallic zinc to precipitate the dissolved precious metals.     

Leaching of oxidic zinc materials with chlorine and chlorine hydrate

Low grade zinc ores and residues were leached in chlorine water and chlorine hydrate water mixtures. It was found that the rate of leaching Adrar ore and Electric Arc Furnace dust obeyed a shrinking core diffusion model, whereas, the rate of leaching of Turkish ore appeared to be controlled by a surface reaction. In all cases, lead leached with the zinc but the iron oxides remained virtually undissolved.     

Bacterial leaching of low-grade ZnS concentrate using indigenous mesophilic and thermophilic strains

In this study low-grade sphalerite has been treated by the bioleaching process using native cultures of Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfido-oxidans in order to determine the ability of these bacteria to the leaching of zinc. The effects of bacterial strain, pH, temperature, pulp density, iron precipitation, and initial concentration of ferric iron on the zinc leaching were evaluated. The bioleaching experiments were carried out in shake flasks at pH 1.5, 180 rpm, 33 °C and 60 °C for mesophilic and thermophilic bacteria, respectively. Compared with the use of laboratory reference strains or control conditions, zinc recovery from the respective concentrate was greater when native isolates were employed. The experimental data show that the selection of the suitable pH and temperature during the bioleaching processes would be important. The results indicate that the increase in pulp density generates a decrease in the dissolved zinc concentration. The maximum zinc extraction reached was 87% using native thermophile S. thermosulfido-oxidans culture after 30 days.     

响应曲面法优化产氨细菌浸矿试验研究

为了研究产氨细菌浸矿条件,采用响应曲面法对产氨细菌浸出碱性铜矿石的工艺条件进行优化,并揭示各因素对铜浸出效果的影响水平及其交互作用规律。研究结果表明,采用响应曲面法的中心组合设计(CCD)模型对试验结果进行回归分析,响应值精确度为98.85%。各因素对铜浸出效果影响的大小为:细菌初始接种量>助浸剂浓度>矿浆浓度。产氨细菌浸出碱性铜矿石最佳工艺条件为:细菌初始接种量30%,矿浆浓度14%,助浸剂浓度0.04 mol/L。在此条件下,浸出144 h后,铜浸出率可达47.32%,比优化前提高了4.67%。     

Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

Leaching of copper and zinc from oxidised ores by fungi

Various types of fungi have been isolated from Indian mine water samples and the leaching of oxidised copper and lead—zinc ores by these species investigated. Metal dissolution characteristics with respect to one specific type of fungi, viz. Aspergillus niger, are illustrated. The effects of pH, pulp density and carbon source on the fungal activity are also reported.     

Kinetics of Dissolution of Tenorite in Ammonium Media

In this work, the dissolution kinetics of tenorite (CuO) in a NH₄OH-H₂O system was studied. The studied temperature range was 5–55°C, ammonium hydroxide concentration between 0.1 and 0.75 M, and a particle size range of 5–24 µm. The stirring speed, pH of the ammonia solution, and various agents were also studied. The results indicated that the leaching of tenorite occurred quickly with a particle size of 5 µm in a 0.45 M solution of NH₄OH for a pH value equal to 10.5. Dissolution of CuO also increases as temperature and the concentration of NH₄OH increase. For concentrations less than 0.10 M, there is almost no leaching tenorite. By decreasing the particle size, the dissolution of CuO increase. Results show the stirring speed had no significant effect on the leaching rate of tenorite for values above 250 rpm. Leaching kinetics was analyzed using the model of the surface chemical reaction. The reaction rate was of the order of 2.2 with respect to the concentration of ammonium hydroxide and inversely proportional to the initial particle size. Activation energy of 59 kJ/mol was estimated for the temperature range of 5–55°C.     

Selective and Efficient Extraction of Zinc from Mixed Sulfide–oxide Zinc and Lead Ore

Mixed sulfide–oxide lead and zinc ores are generally composed of both sulfides and oxides. The dissolution of sulfides is more difficult than oxides thus the addition of oxidant is necessary. In this paper, oxidative leaching of mixed ore in NH₃-(NH₄)₂SO₄ solution using ammonium persulfate as oxidant under atmospheric pressure and relatively low temperature was investigated for the first time. The effects of factors on the leaching of pure ZnS were studied and the optimal conditions with zinc 98.7% were determined. Selective and efficient extractions of 93.9% and 94.9% zinc from zinc sulfide ore and mixed ore were also achieved, respectively.     

Optimisation of different physical parameters for bioleaching of phosphate by Aspergillus niger from Indian rock phosphate

A mutant strain of Aspergillus niger AB100 was incubated with samples of rock phosphate. Mutation resulted in a greater amount of solubilisation (30 to 35%) as against the parent strain (10 to 15%). The influence of leaching parameters such as ore concentration (pulp density), particle size, initial pH of the medium, temperature, volume of the medium in 250 ml flasks, inoculum concentration and age of inoculum was studied. When low quantity of rock phosphate is applied (0.1%) the solubilisation of phosphorus was optimal (40.5%). Optimum particle size was--200 to 240 mesh, initial pH of the medium 4.0, optimum volume of the fermentation medium 160 ml, time period of incubation was 8 days, inoculum volume was 7.5 ml, and age of inoculum 7 days. The maximum leaching of phosphorus by using these optimum physical parameters is 45 to 50%.     

The ferric fluosilicate leaching of lead concentrates: Part I. Kinetic Studies

A new hydrometallurgical leaching process, which dissolves lead concentrates with acidified ferric fluosilicate solution, has been investigated for the selective extraction of lead and zinc from lead concentrates containing galena. The leaching of the Pine Point lead concentrate by ferric fluosilicate solutions was studied under various experimental conditions in the temperature range 20 °C to 95 °C. Temperature had a pronounced effect on the dissolution of the concentrates. The rates of lead leaching are very rapid over the temperature range 38 °C to 95 °C. The kinetics of zinc extraction are much lower than those of lead extraction. The reaction rates for the dissolution of galena were found to be controlled by surface chemical reaction. The apparent activation energy of the leaching reaction was calculated to be 62.1 kJ/mol. The initial concentrations of Pb²⁺, H⁺, and Fe³⁺ in the lixiviant do not have a significant effect on the rate or extent of lead extraction under the experimental conditions in this study.     

Column Bioleaching of a Low-Grade Silicate Ore of Uranium

The bioleaching of a low-grade Indian uraninite ore (triuranium octoxide, U₃O₈: 0.024%), containing ferro-silicate and magnetite as the major phases, and hematite and pyrite in minor amounts, has been reported. Experiments were carried out in laboratory scale column reactors inoculated with enriched culture of Acidithiobacillus ferrooxidans isolated from the source mine water. The pH effect on uranium recovery was examined with the same amounts of ores in different columns. With the presence of 10.64% Fe in the ore as ferro-silicate, the higher uranium biorecovery of 58.9% was observed with increase in cell count from 6.4 × 10⁷ to 9.7 × 10⁸ cells/mL at pH 1.7 in 40 days as compared to the uranium recovery of 56.8% at pH 1.9 with a corresponding value of 9.4 × 10⁸ cells/mL for 2.5-kg ore in the column. The dissolution of uranium under chemical leaching conditions, however, recorded a lower value of 47.9% in 40 days at room temperature. Recoveries were similar with 6-kg ore when column leaching was carried out at pH 1.7. The bioleaching of uranium from the low-grade ore of Turamdih may be correlated with the iron(II) and iron(III) concentrations, and redox potential values.     

Preparation of Industrial Manganese Compound from a Low-Grade Spessartine Ore by Hydrometallurgical Process

The increasing global demands for pure manganese in steel production and manganese compound as dietary additives, fertilizer, pigment, cells and fine chemicals production cannot be over-emphasized. Thus, continuous efforts in developing low cost and eco-friendly route for purifying the manganese ore to meet some defined industrial demands become paramount. Therefore, this study focused on reductive leaching and solvent extraction techniques for the purification of a Nigerian manganese ore containing admixture of spessartine (O_96.00Mn_24.00Al_16.00Si₂₄.₀₀) and quartz (Si_3.00O_6.00). During leaching, parameters such as leachant concentration and reaction temperature on the extent of ore dissolution were examined accordingly for the establishment of extraction conditions. At optimal leaching conditions (1.5 mol/L H₂SO₄?+?0.2 g spent tea, 75 °C), 80.2% of the initial 10 g/L ore reacted within 120 min. The derived dissolution activation energy (Ea) of 35.5 kJ/mol supported the diffusion reaction mechanism. Thus, the leachate at optimal leaching was appropriately treated by alkaline precipitation and solvent extraction techniques using sodium hydroxide and (di-2-ethylhexyl) phosphoric acid (D2EHPA) respectively, to obtain pure manganese solution. The purified solution was further beneficiated to obtain manganese sulphate monohydrate (MnSO₄.H₂O, melting point?=?692.4 °C: 47-304-7403) of high industrial value. The unleached residue (~?19.8%) analyzed by XRD consisted of silicileous impurities (SiO₂) which could serve as an important by-product for some defined industries.     

EFFECT OF CERTAIN SURFACTANTS ON THE LEACHING AND PRECIPITATION PROCESSES IN ZINC FERRITE RESIDUE TREATMENT

The effect of a surfactant mixture of nonylphenolpolyethylene glycol (D1), dinaphthylmethane-4,4′-disulphonic acid (D2), and polyethylene glycol with molecular weight 400 (D3) on the dissolution of zinc and metal impurities present in zinc ferrite residue in dilute sulfuric acid (160 g L^?1 H₂SO₄) as well as on both jarosite and goethite precipitation was studied at 90°C. The following influences of the surfactant mixture (D1 + D2 + D3), determined by comparing the results obtained in the presence and absence of surfactants, were found. Adsorption of surfactants on zinc ferrite residue surface decreases the dissolution of zinc and metal impurities (Fe, Cu, Cd, As, Sb, and Co). Their extraction efficiencies at the end of the super hot leaching process carried out with surfactants are 4.85–6.29% lower than without them. The formation of a sulfur “sponge” layer on the surface of liquor during the dissolution of ZnS present in zinc ferrite residue is hindered by the surfactants due to their effect as wetting agents and sulfur dispersants. The presence of surfactants reduces the amount of zinc and metal impurities (Fe, Cu, Cd, and As) remaining in the solution after jarosite or goethite precipitation by 5.33–5.86% or 8.03–9.93%, respectively. The volume of jarosite and goethite precipitates increases in the presence of surfactants due to their effect as wetting and flocculation agents. On the other hand, D1 and D3 act as complexing agents. The abovementioned effects of surfactants improve the sorption capacity of both jarosite and goethite, thus ensuring better purification of zinc sulphate solutions, but hindering zinc leaching.     

某难处理金矿热压氧化渣预处理试验研究

高铜难处理金矿经酸性热压氧化后,铜基本被浸出进入溶液中,消除了铜对氰化过程的影响,而银在热压处理过程中易与生成的黄钾铁矾相结合,生成难处理的银铁矾[AgFe₃（SO₄）₂（OH）₆],在随后的常规氰化试验中,金回收率达99%以上,但银回收率不足10%。针对银回收率低的问题,系统考察了矿浆浓度、NaCN浓度、石灰用量、预处理温度和时间、氰化时间及炭密度等因素对金、银浸出率的影响,进而确定了最佳浸出条件。试验结果表明：在85~90 ℃、矿浆浓度为40%、石灰用量为40 kg/t的条件下,对氧化渣进行碱性预处理,随后在NaCN用量为0.10%的条件下浸出8 h,银回收率得到大幅提高（达到85%）,金浸出率也保持在99%以上。     

The bioleaching of different sulfide concentrates using thermophilic bacteria

The bioleaching of different mineral sulfide concentrates with thermophilic bacteria (genusSulfolobus @#@) was studied. Since the use of this type of bacteria in leaching systems involves stirring and the control of temperature, the influence of the type of stirring and the pulp density on dissolution rates was studied in order to ascertain the optimum conditions for metal recovery. At low pulp densities, the dissolution kinetic was favored by pneumatic stirring, but for higher pulp densities, orbital stirring produced the best results. A comparative study of three differential concentrates, one mixed concentrate, and one global concentrate was made. Copper and iron extraction is directly influenced by bacterial activity, while zinc dissolution is basically due to an indirect mechanism that is activated in the presence of copper ions. Galvanic interactions between the different sulfides favors the selective bioleaching of some phases (sphalerite and chalcopyrite) and leads to high metal recovery rates. However, the formation of galvanic couples depends on the type of concentrate.     

Effect of pH,iron concentration,and pulp density on the solubilization of uranium from ore material in chemical and microbiological acid leach solutions: Regression equation and confidence band analysis

The solubilization of uranium from a finely ground ore material was investigated in leaching tests each lasting for about 24 h. Ferric iron, added as Fe₂(SO₄)₃ or produced by prior microbiological oxidation of FeSO₄, accelerated the rates of uranium leaching, as compared with those obtained with sulfuric acid or acidic ferrous sulfate. Pulp density and initial pH were also test variables. Yields of up to 100% uranium extraction were obtained within 24 h. Quadratic response surfaces were fitted to the experimental leach curves and confidence bands were calculated to assess the significance of the effects of pH, iron concentration, and pulp density on uranium solubilization. The general separation of the confidence bands indicated that each factor had a significant effect.     

Dried leaves — Novel reductant for acid leaching of manganese ore

In the present investigation results on the use of dried leaves as a reductant for manganese ore leaching is reported. A complete flow-sheet consisting of steps such as reductive acid leaching, enrichment of leach solution by recycling, iron removal and crystallization has been developed for the preparation of manganese sulphate monohydrate from manganese ore of Gujarat Mineral Development Corporation (GMDC), Ahmedabad, India. During leaching effects of pulp density, amount of acid, temperature, particle size of ore and reductant to ore ratio were studied. Almost total manganese extraction could be achieved under the following conditions: leaching time 8h, H₂SO₄ 5% (v/v), pulp density 10% (w/v), temperature 950C and dried leaves to ore ratio 0.5. Mn enriched (> 90 g/L Mn) leach liquor was obtained by recycling the leach solution twice. The solution so obtained was purified by pH adjustment using lime slurry. A schematic flowsheet for the preparation of manganese sulphate monohydrate crystal is given.     

LEACHING OF MASSIVE RICH COPPER ORE WITH ACIDIFIED FERRIC CHLORIDE

Massive rich copper ore, taken from the Küre region of Turkey and containing 7.95% Cu, 2.13% Pb, 0.341% Zn, 0.087% Co, 0.039% Ni, 0.9 (g/t) Au, and 17 (g/t) Ag, was subjected to the experimental study. Effects of leaching time, ferric ion concentration, solid/liquid ratio, acid concentration and temperature on the metal dissolution efficiencies were investigated in order to determine optimum leaching conditions and related leaching kinetics. As a result of these experiments carried out under the optimum leaching conditions, 76% of Cu, 55% of Co, 96% of Ni, 100% of Pb, and 91% of Zn were extracted. The value of apparent activation energy for copper dissolution was found as 43.8?kJ/mole, which is in agreement with the published data. The rate-controlling step was found as the diffusion of ferric ions into the sulfur layer formed on the surface of partially leached ore particles.